为什么Ruby 1.9.2中的to_s会改变行为？

Question

It looks like in ruby 1.9.2 if to_s is defined, inspect will return to_s?? Why would this change?

This:

class ToSClass
  def to_s
    "#{self.class.name} to_s called"
  end
end
class InspectClass
  def inspect
    "#{self.class.name} inspect called"
  end
end
class BothClass
  def inspect
    "#{self.class.name} inspect called"
  end
  def to_s
    "#{self.class.name} to_s called"
  end
end

c1 = ToSClass.new
puts c1.inspect
puts c1.to_s
c1 = InspectClass.new
puts c1.inspect
puts c1.to_s
c1 = BothClass.new
puts c1.inspect
puts c1.to_s

outputs this:

ToSClass to_s called
ToSClass to_s called
InspectClass inspect called
#<InspectClass:0x316baf8>
BothClass inspect called
BothClass to_s called

Answer 1

Object#inspect will call to_s if available. I don't think the behavior has changed.

I've run your program on 1.9.2 and 1.8.7 and don't see any difference.

$ rvm inspect.rb 1.9.2,1.9.1,1.8.7

info: 1.9.2 (ruby-1.9.2-p0): ruby 1.9.2p0 (2010-08-18 revision 29036) [x86_64-linux] 

ToSClass to_s called
ToSClass to_s called
InspectClass inspect called
#<InspectClass:0x00000001941c80>
BothClass inspect called
BothClass to_s called

info: 1.9.1 (ruby-1.9.1-p378): ruby 1.9.1p378 (2010-01-10 revision 26273) [x86_64-linux] 

ToSClass to_s called
ToSClass to_s called
InspectClass inspect called
#<InspectClass:0x000000011594b8>
BothClass inspect called
BothClass to_s called

info: 1.8.7 (ruby-1.8.7-p302): ruby 1.8.7 (2010-08-16 patchlevel 302) [x86_64-linux] 

ToSClass to_s called
ToSClass to_s called
InspectClass inspect called
#<InspectClass:0x7ffd795afd60>
BothClass inspect called
BothClass to_s called